Progressive mitochondrial oxidative damage and dysfunction is fundamental to the pathogenesis of many human diseases. Using a yeast model system, we have shown that the novel protein Lifespan-associated Mitochondrial Stress-responsive 1 (Lms1) is recruited to mitochondria under conditions of mitochondrial stress. When Lms1 is depleted, oxidative stress induces loss of respiratory function and markedly accelerated loss of viability over time. Lms1 associates in vivo with Cdc48, an ATPase integral to the retrotranslocation and degradation of proteins from the endoplasmic reticulum (ERAD pathway). These observations have been extended to C. elegans, wherein knockdown of Lms1 leads to peroxide sensitivity and decreased lifespan and oxidative stress induces cytosol to mitochondria translocation. We propose that Lms1 is a component of an important pan-eukaryotic system for protection from the lethal effects of oxidative stress and mitochondrial dysfunction. We hypothesize that it senses mitochondrial stress and, through Cdc48 recruitment, enacts the degradation of misfolded or damaged mitochondrial protein. We hereby propose to determine: I) The mechanisms regulating Lms1 mitochondrial translocation. We will determine: 1) the location and specificity of the mitochondrial dysfunction signal; 2) how this signal is relayed to Lms1; and 3) the identity of the Lms1 mitochondrial receptor. II) The function of Lms1 in preserving mitochondrial activity and viability. We will: 1) comprehensively identify the components of the Lms1- Cdc48 complex; 2) determine the nature and regulation of the Lms1-Cdc48 interaction; and 3) understand the mitochondrial defect observed in the lms1 mutant. III) Lms1 regulation and function in mammals. We will: 1) examine mammalian Lms1 regulation and function using cultured cells; and 2) using an Lms1-/- mouse, determine the physiological role of this protein in maintaining mitochondrial function, particularly in cardiomyocytes. PUBLIC HEALTH RELEVANCE: Many human diseases are caused by a progressive deterioration of the function of mitochondria. We have discovered a widespread cellular system that acts to prevent this type of deterioration and have shown that it protects both yeast and nematodes from certain types of damage. We suggest that it will be equally important in humans and propose to further understand its biochemical and physiological role.